A molding device for molding a preform to form a hollow container is generally loaded with a heating device for heating the preform to a temperature at which the preform is moldable. This heating device is provided on a transport line, on which the preform is transported, to heat the preform to a predetermined temperature while transporting it. Such a heating device is equipped with various heaters, such as infrared heaters, and the preform passing through the interior of the device is heated with light (heat) from the heaters, and is also heated with an atmosphere within the device raised in temperature by the heaters.
If the atmosphere within the heating device excessively rises in temperature, however, it may be impossible to heat the preform to an appropriate temperature. For example, even when it is attempted to impart a temperature distribution at different sites in the axial direction of the preform, it is unlikely to provide an appropriate temperature distribution, if the atmosphere within the device is raised in temperature excessively.
Among heating devices for a preform, therefore, there is one which is configured to cool the preform with a cooling wind, and release air within the heating device to the outside, thereby suppressing an excessive temperature rise within the device. For example, a heating device is available which is adapted to cool the preform with cooling air blown from a blow-off port into a heating oven, and which has a wire netting on the top surface (upper part) of the heating oven for letting air in the heating oven escape to the outside of the oven to adjust the temperature within the heating oven (see Patent Document 1). There is another heating device, for example, which is designed to bring the interior of a tunnel, where the preform is transported, to reduced pressure by means of a blower, thereby drawing cooling air into the tunnel and discharging air heated within the tunnel (see Patent Document 2).
By so discharging air within the heated device (inside the heating oven, or inside the tunnel) to the outside, an excessive temperature rise of the atmosphere within the device can be suppressed.